A typical starter motor for an internal combustion engine includes a pinion which is mounted rotation with the motor drive shaft and is also mounted to move axially on the shaft. On operation of the starter motor, the pinion will be moved axially along the drive shaft into engagement with the ring gear on the flywheel of the engine. When the engine starts, the flywheel rotates the pinion at an increased speed, overriding the speed of the starter shaft and moving the pinion back to its original axial starting position, out of engagement with the ring gear teeth.
The meshing of the teeth of the pinion with the teeth of the ring gear occurs by lateral insertion of the pinion teeth into the ring gear teeth. As the pinion teeth enter the teeth of the ring gear, both radial torque and axial impact force are imparted to the teeth of the pinion.
Because of this, the conventional starter motor includes a cushioning mechanism which will absorb the shock caused by engagement of the pinion teeth with the teeth of the ring gear and permit the teeth to align without damage to the starter or engine structure. In the typical starter motor construction, the pinion is formed of a metal that is harder and more wear resistant than the metal of the gear ring on the flywheel and the cushioning mechanisms, as used in the past, have been designed to prevent chipping or other damage to the teeth of the flywheel gear ring.